1. Field of the Invention
The present invention relates in general to an optical pickup system used in, for example, a compact disc player, for reading data recorded on an optical disc, and more particularly to an optical pickup system using a holographic optical element in order to achieve the recent trend of miniaturization and lightness.
2. Description of the Prior Art
Recently, the use of optical discs such as compact discs and laser discs has greatly increased. In the future, these optical discs will be used in all technical fields, by virtue of being able to store a lot of information and being convenient to use.
Such optical discs require an optical pickup system for reading information recorded thereon.
With reference to FIG. 1, a known optical pickup system comprises a semiconductor laser 3 used as a light source, and a half mirror 2 reflecting the laser beam emitted from the semiconductor laser 3. In order to read the information recorded on an optical disc 1, the laser beam reflected by the half mirror 2 is focused on the disc 1. To achieve the above object, a 45.degree. reflection mirror 4 and a focusing lens 5 are positioned between the half mirror 2 and the optical disc 1. Here, the 45.degree. reflection mirror 4 reflects the laser beam reflected by the half mirror 2 to the focusing lens 5 which focuses the laser beam on the disc 1. The known optical pickup system further includes a condensing lens 6 which condenses the laser beam, reflected by the optical disc 1, to a photo detector 7 which detects the condensed laser beam so as to read the information recorded on the disc 1.
In the above optical pickup system, the laser beam emitted from the laser diode 3 is reflected by the half mirror 2 and in turn focused on the optical disc 1 by way of the 45.degree. reflection mirror 4 and the focusing lens 5.
The laser beam focused on the optical disc 1 is, thereafter, reflected by the disc 1 and varies in its light intensity in accordance with different shapes of the recorded bumps or pits of the optical disc 1. The laser beam reflected by the disc 1 passes through the above optical path in reverse. That is, the reflected laser beam is transmitted through the half mirror 2 and condensed by the condensing lens 6 to the photo detector 7 adapted for detecting laser beam.
The intensity of the laser beam condensed by the condensing lens 6 is detected by the photo detector 7, thereby achieving the reading of the information recorded on the optical disc 1.
However, the known optical pickup system undesirably has a relatively large volume since the optical elements are spaced at individual intervals. Additionally, the semiconductor laser 3 and the photo detector 7 are separately provided in the optical pickup system and this makes the size of the pickup system be larger and the weight of the pickup system be heavy. Also, a relative long time elapses until the laser beam, reflected to and focused on the optical disc 1, reaches the photo detector 7, As a result known optical pickup system performs the information reading operation slowly.
Furthermore, all the elements of the known pickup system should be separately mounted and this requires a longer assembling time, which results in a increase of the manufacturing cost of the system.